1. Field of the Invention
The present invention relates to a magnetic head used in a magnetic disk apparatus for recording information on and reproducing information from a recording medium.
Recently, as the size of a magnetic disk apparatus has been reduced and the storage capacity thereof has been enlarged, the recording density of a recording medium has become high, and thus a magnetic head which floats low over the disk (small clearance) is required. However, because of the requirement that the magnetic head be resistant to shock, there is also a need to reduce occurrences of contact between the magnetic head and the disk.
2. Description of the Related Art
FIGS. 1A, 1B and 1C show a construction of a conventional magnetic head. Referring to FIG. 1A, two rail surfaces 13a and 13b are formed on the surface of a core slider 12 of a magnetic head 11, which surface faces a magnetic disk (recording medium). The rail surfaces 13a and 13b are made to extend in the direction in which air flows. Tapered surfaces 14a and 14b which allow the head to float are formed on the side at which air enters the space between the head and the disk.
On an end face of the rail surface 13a at which face air exits the space between the head and the disk, a thin-film element 15 for writing and reading information is provided. As shown in FIG. 1B, the thin-film element 15 is formed such that an insulating film (alumina) 16 is formed on the end face of the core slider 12 (rail surface 13a), and a magnetic film 17 is formed on the insulating film 16. An insulating film 18 is formed on the magnetic film 17, and a coil 19 is provided in the insulating film 18. A magnetic film 20 is formed on the insulating film 18. Recording and reproduction are performed in a gap 22 formed between the magnetic film 17 and the magnetic film 20. A protective film (insulating film) 21 is formed on the magnetic film 20 in the thin-film element 15. The shaded area indicates that portion of the protective film which is susceptible to temperature increase.
The rail surfaces 13a and 13b are chamfered (applied with a lapping process) as indicated by broken lines in FIG. 1C so as to allow air to flow smoothly. Both the width and height of the chamfering are 0-10 .mu.m. A distance L between the end face of the core slider 12 and the end of the protective film 21 is set such that L.gtoreq.0.025 mm. A distance S (thickness of the protective film) between the magnetic film 20 and the end of the protective film 21 is set such that S.apprxeq.0.015-0.02 mm.
The magnetic head 11 is enabled to float over the magnetic disk by receiving an air flow generated by the rotating magnetic disk. In order that damage caused by the contacting of the magnetic head 11 with the magnetic disk be minimized, a thin film of DLC (diamond-like carbon) or the like may be provided on the rail surfaces 13a and 13b (including the tapered surfaces 14a and 14b) and/or on the magnetic disk, or burrs created by the chamfering of the rail surfaces 13a and 13b may be removed.
FIG. 2 explains thermal expansion of the protective film of the conventional magnetic head. Referring to FIG. 2, when the magnetic head 11 is driven for a recording operation, the temperature of the thin-film element 15 rises because a current is fed to the coil 19, with the result that the protective film 21 swells due to thermal expansion, as indicated by a shaded end part 21' in FIG. 2. For example, it was experimentally found that a swelling of the protective film 21 of alumina measured 6 nm per temperature rise of 10.degree. C.
Hence, the narrowest achievable separation (clearance) between the magnetic head 11 and the magnetic disk depends on the magnitude of the swelling of the protective film 21 and on the spacing between the head and the disk. Accordingly, frequent contacts between the head and the disk may occur. Powder created from abrasion damages the thin-film element 15 and the disk. Therefore, it becomes difficult to secure small clearance.
Further, the chamfering of the rail surfaces 13a and 13b of the core slider 12 is done after a wafer having the thin-film element 15 formed thereon is cut and the rail surfaces 13a and 13b are formed. If the chamfering process is applied to the thin-film element 15, a variation in the quality of the produced head results. For example, the electromagnetic transducing property may deteriorate.
Furthermore, the conventional magnetic head is liable to be affected by a fine projection located on the magnetic disk. If the magnetic head is affected by such a fine projection, an abnormal signal will be superimposed on the read signal, as will be described in detail later.